Corrugated Microfiber Webs
Corrugated and pleated webs of polymeric microfiber are known in the art and have been disclosed in the following U.S. Pat. Nos.: 5,038,775, 4,939,016, 4,910,064, 4,842,739, 4,826,642, 4,774,001, 4,759,782, 4,676,807, and 4,617,124.
U.S. Pat. No. 5,038,775 discloses a filter assembly that includes a pleated microfibrous web as a filter medium. The filter medium is maintained in a pleated condition by a scrim that extends over the upstream and downstream sides of the pleated filter medium to provide substantially continuous support to the filter medium.
U.S. Pat. No. 4,939,016 discloses a composite web material that includes a hydraulically entangled laminate of melt blown microfibers and a further layer, preferably at least one of pulp fibers, staple fibers, melt blown fibers, and continuous filaments, with or without particulate material. The patent discloses that this composite web can be formed into a corrugated stretchable fabric by pre-stretching the web and hydraulically entangling the web while stretched.
U.S. Pat. No. 4,910,064 discloses a nonwoven web that has a multiplicity of substantially longitudinally molecularly oriented continuous filaments of a thermoplastic polymer. Onto the longitudinal continuous filaments are deposited a multiplicity of melt blown fibers having fiber diameters of 0.5 to 50 micrometers (.mu.m). The melt blown fibers form bonds at some of their intersections with the longitudinal continuous filaments to stabilize and fix the orientation of those filaments. The stabilized continuous filaments are pleated or corrugated and are stabilized in that condition by depositing a layer of melt blown fibers on one side of the pleats or corrugations (column 26, lines 12-16).
U.S. Pat. No. 4,842,739 discloses a high surface area filter cartridge that contains a nested arrangement of disk-shaped filter layers. The disk-shaped filter layers have a pattern of regular radial pleats and comprise a laminate that includes an upstream prefilter layer, a filtration media, and a downstream cover layer. The filtration media can be a nonwoven web of melt blown microfibers. The filter laminate is pleated by an embossing operation.
U.S. Pat. Nos. 4,826,642 and 4,774,001 disclose a composite structure that is useful as a flat filtration medium or as a pleated (corrugated) filtration structure. The composite structure comprises a microporous membrane and a synthetic thermoplastic web of microfibers secured to the microporous membrane by melt blowing the microfibers thereon.
U.S. Pat. Nos. 4,759,782 and 4,676,807 disclose a cylindrical filter structure that may comprise a single pleated filter medium supported by an outer perforated, cylindrical support cage. The filter media may comprise organic melt blown microfibers. In Example 1, a composite, cylindrical pleated filter structure was prepared from two layers of melt-blown polyester fibrous material having two glass fiber layers sandwiched therebetween. The melt-blown polyester fibrous material contained fibers having diameters ranging from 35 to 50 .mu.m, and was calendared to a thickness of 0.009 inches (pore size was 100 .mu.m) before being combined with the glass fiber medium. The composite structure was placed in pleated form in a perforated polypropylene cage. No disclosure is provided as to how the composite structure is pleated.
U.S. Pat. No. 4,617,124 discloses a polymeric, microfibrous filter sheet where the microfiber is coated with a cured thermosetting binding resin or polymer. In column 24, lines 29-31, it is disclosed that the filter sheet can be placed in pleated form and incorporated into a cartridge.
Face Masks
Nonwoven webs of polymeric microfiber have been commonly used in face masks as filtration layers. U.S. Pat. Nos. 4,807,619, 4,536,440, 4,215,682, and 3,802,429 disclose cup-shaped face masks that have nonwoven webs of polymeric microfiber as filtration layers.
Face masks have been disclosed that have corrugated or pleated surfaces. U.S. Pat. Nos. 4,807,619, 4,641,645, 4,536,440, 4,248,220, 3,985,132, 3,220,409, and EP-A 0,149,590 A3 disclose such face masks. Of these patents, only U.S. Pat. No. 4,641,645, however, discloses a filter that includes a corrugated nonwoven web of polymeric microfiber. In U.S. Pat. No. 4,641,645, the face mask has a middle layer of polymeric microfiber disposed coextensively between two polyester nonwoven webs. All three layers are assembled into a composite mat and molded into a cup-shaped configuration having a plurality of tightly-compacted rib elements. While the tightly-compacted rib elements have peaks and valleys that provide the face mask with a corrugated effect, the tightly-compacted rib elements are employed to give the face mask structural strength (not to improve filtration performance), and they reduce the loftiness of the middle layer of polymeric microfiber and also do not substantially increase the effective surface area of the filter.
A number of different approaches have been taken to increase the effective filtering surface area of a face mask; see, for example, U.S. Pat. Nos., 4,883,547 and 4,827,924, and EP-A 0,469,498 A2. EP-A 0,469,498 A2, in particular, discloses a particle-filtering half mask that has a folded filter layer disposed between exterior and interior cover layers. The folded filtering layer is made of a porous, flexible filtering material that is folded in an overlapping arrangement. A holding strip extending transverse to the fold direction is glued to the folds to ensure that they lie flat. Other than indicating that the filter layer may be a multi-layer fiber fleece, EP-A 0,469,498 A2 does not disclose the composition of the filtering material. Nor does the document disclose how the filtering layer is placed in a folded condition, and no disclosure is made in regard to preserving the loft of the filtering material during the manufacture of the folded filter.
Thermal Insulation
Nonwoven webs that contain polymeric microfiber are known to be useful as thermal insulation. U.S. Pat. No. 4,118,531 to Hauser discloses a nonwoven web that contains polymeric microfiber intermixed with crimped staple fiber. This nonwoven web demonstrates very good thermal resistance but lacks sufficient integrity to allow the web to be adhesively bonded to another surface and to allow the web to maintain a cohesive structure after being subjected to abrasion. Used as insulation for footwear and gloves and other apparel, the nonwoven web can be exposed to abrasion that can cause the web to be released from the surface to which it is adhered and also may cause the web to lose structure and form clumps in the apparel. To overcome these problems, the nonwoven web may be embossed. Embossing, however, compresses the web and reduces its loft and therefor lowers its thermal resistance. To raise the overall thermal resistance, more layers of embossed web must be employed, having the undesirable result of increasing the weight and cost of the apparel.
Corrugating Apparatus
Legions of corrugating apparatuses have been disclosed in the past century. The corrugating apparatus art is replete with devices that employ mating gears to corrugate a flat web; see, for example, U.S. Pat. Nos. 4,116,603, 3,998,140, 3,905,857, 3,792,952, 3,723,213, 3,157,551, 3,025,963, 2,051,025 and 1,290,800. Reciprocating corrugating devices also are well known in the corrugating apparatus art; see, for example, U.S. Pat. Nos. 4,650,102, 4,239,201, and 1,822,509. More recently, in U.S. Pat. No. 4,874,457 a corrugating apparatus has been disclosed which corrugates a flat web by (i) introducing the flat web onto the ends of radially-extending paddles and then (ii) moving the ends of the radially-extending paddles towards each other to cause the web to corrugate. The paddles move about a path that has a curved portion and a straight portion, and the apparatus corrugates the flat web when the paddles move from the curved portion of the path to the straight portion. The web is maintained in a corrugated condition by passing the web under an oven to bond adjacent folds of the corrugated web together. An optional cover layer can be introduced onto the tops of the corrugations and also is passed under the oven to fuse the cover layer to the corrugations to stabilize the corrugated web.